How cell cycle events are controlled with growth remains an important and perhaps the most important, outstanding question in prokaryotic biology. A group of conserved and essential GTPase proteins, related to Ras, have been implicated in cell cycle control but remain poorly characterized. The study of the Obg GTPase has the potential to elucidate aspects of the mechanism of chromosome segregation in bacteria, which is not, at present, understood. Because Obg is universally conserved and essential, its function has impacts on all bacteria, including bacterial pathogens, and constitutes a potential target for antibiotic therapy. All eukaryotic cells possess Obg, too-its function may be essential for mitochondria-and therefore its role in eukaryotic cell biology will be important to understand and will be facilitated by studies first in prokaryotes. An integrative approach, combining cell visualization, genetics, biochemistry and physiology, provides an opportunity to make headway into understanding these important and complex problems. The connection between translational stress and cell cycle will be investigated. The hypothesis that SeqA binding to the chromosome controls access to replication initiation and chromosome segregation machinery will be tested. Additional factors in the stringent response control of cell cycle will be sought. Using state-of- the-art fluorescence microscopy, the localization of the E. coli Obg protein will be examined, as well as its impact on bacterial cytoskeleton, including the actin-related MreB helical filament, and the organization of the chromosome and replisome. The interaction of the ObgE protein with several proteins, including those controlling replication initiation and chromosome segregation, processes on which Obg may exert control, will be probed. Several genetic screens will explore the role of ObgE and the DNA binding protein, SeqA in the regulation of DNA replication and chromosome segregation. Finally, the association of ObgE with the ribosome will be studied, as well as the impact of the stringent response and ObgE on ribosome function and stability. LAY DESCRIPTION: We will study a protein present in all bacteria that appears to control their growth. This will provide important missing information about how bacteria divide and may provide a target for antibiotics.